(1) Field of the Invention
The present invention is directed toward ion exchange filters useful in fuel cell systems, fuel cell systems including ion exchange filters and methods for treating fluid of fuel cells.
(2) Description of the Related Art
The design and operation of fuel cells are well known in the art. Fuel cells generate electricity through an electrochemical oxidation of a fuel, e.g. hydrogen, methanol, etc. Unreacted fuel and/or oxidant (exhaust) are often recycled and reintroduced into the fuel cell. Recycled constituents may be filtered with ion exchange filters to remove contaminates prior to being reintroduced into the fuel cell. Such contaminates include degradation and/or elution products of various system components, e.g. membrane, piping, coolant, catalysts, etc., along with impurities that may be introduced with the fuel and oxidant. By way of example, US 2007/0259241 describes a fuel cell system including a hydrogen recycle system for directing unreacted hydrogen exhaust and water from the fuel cell to gas-liquid separator. The resulting exhaust gas is then passed through an ion exchange filter prior to being recycled back to the fuel cell for subsequent reaction. JP 2005/339814A describes a similar fuel cell system including a hydrogen recycle system including an ion exchange filter.
Fuel cell systems often including coolant systems which circulate coolant fluid between a fuel cell and a heat exchanger. Ion exchange filters are also used in such coolant systems to remove debris and elution products from the recirculation coolant. Examples of such systems are described in: U.S. Pat. No. 7,261,816; U.S. Pat. No. 6,673,482; U.S. Pat. No. 6,663,993; US 2004/0028971 and EP 1 791 206.
Ion exchange filters used in such fuel cell applications typically comprise a cartridge including fluid flow passages to permit fluid of a fluid circuit to pass through. A wide variety of cartridges are known including those described in U.S. Pat. No. 7,261,816 and JP 2005/339814A. A cartridge can be combined with a gas-liquid separator as described in US 2007/0259241. The cartridge contains an ion exchange resin which removes ions or other charged constituents from the fluid passing in contact with the resin. JP 2002-343388 describes the use of a mixed bed of ion exchange resins for filtering product water and/or coolant within a phosphoric acid fuel cell.
Given the high operating temperatures of fuel cells, the ion exchange resins used in such systems must have high temperature stability, i.e. the resin must maintain ion exchange capacity even after prolonged exposed to high temperatures, e.g. temperatures above about 80° C. and in many instances temperatures above 100° C. or even 120° C. JP 2002-343388 describes a class of anion exchange resins in hydroxide (OH−) form for use in such applications.
In addition to being exposed to high operating temperatures, ion exchange filters of fuel cell systems may also be exposed to repeated freeze/thaw conditions—particularly with respect to vehicle mounted fuel cell systems. Repeated freezing and thawing creates mechanical forces that tend to break-up ion exchange resins and result in undesired pressure drop within the fluid circuit.